The doctrine of plant immunity

Main article: Plant immunity

Vavilov divided plant immunity into structural (mechanical) and chemical. Mechanical immunity of plants is determined by the morphological characteristics of the host plant, in particular, the presence protective devices, which prevent pathogens from entering the plant body. Chemical immunity depends on the chemical characteristics of plants.

vavilov immunity plant selection

Creation of N.I. Vavilov modern doctrine of selection

Systematic study of the world's most important plant resources cultivated plants radically changed the understanding of the varietal and species composition of even such well-studied crops as wheat, rye, corn, cotton, peas, flax and potatoes. Among the species and many varieties of these cultivated plants brought from expeditions, almost half turned out to be new, not yet known to science. The discovery of new species and varieties of potatoes has completely changed the previous understanding of the source material for its selection. Based on material collected by expeditions of N.I. Vavilov and his collaborators, the entire selection of cotton was founded, and the development of humid subtropics in the USSR was built.

Based on the results of a detailed and long-term study of the varietal riches collected by the expeditions, differential maps of the geographical localization of varieties of wheat, oats, barley, rye, corn, millet, flax, peas, lentils, beans, beans, chickpeas, chickpeas, potatoes and other plants were compiled . On these maps one could see where the main varietal diversity of the named plants is concentrated, i.e. where to draw raw material for breeding this crop. Even for such ancient plants as wheat, barley, corn, cotton, which have long settled throughout to the globe, it was possible to establish with great accuracy the main areas of primary species potential. In addition, it was established that the areas of primary formation coincided for many species and even genera. Geographical study has led to the establishment of entire cultural independent floras specific to individual regions.

The botanical and geographical study of a large number of cultivated plants led to the intraspecific taxonomy of cultivated plants, resulting in the works of N.I. Vavilov “Linnaean species as a system” and “The doctrine of the origin of cultivated plants after Darwin.”

In the presence of a viable pathogen and all necessary conditions for infection. In practice, they often talk about disease resistance, which can be characterized as the genetic property of some plants to be affected by the disease to a weak degree. Immunity is absolute, resistance is always relative. Like immunity, resistance is determined by the characteristics of the genome, and there are genes for resistance not only to pathogens, but also to unfavorable environmental factors.

The direct opposite of immunity is susceptibility—the inability of a plant to resist infection and spread of a pathogen. In some cases, a plant that is susceptible to some pathogens may be tolerant or hardy to others, i.e. it does not reduce or slightly reduces its productivity (the quantity and quality of the harvest) when infected.

There are specific and nonspecific immunity. The first manifests itself at the cultivar level in relation to certain pathogens and is also called varietal immunity. Second, or nonspecific (species) immunity can be defined as the fundamental impossibility of a given plant species to become infected specific types pathogens or saprotrophs. For example, a tomato is not affected by the causative agents of smut diseases of cereals, a cucumber is not affected by cabbage clubroot, pepper is not affected by the causative agent of apple scab, etc.

Immunity can be congenital or acquired. Innate, or natural, immunity is controlled genetically and is inherited. It can be passive or active. Passive immunity is determined by the constitutional characteristics of the plant only and does not depend on the characteristics. Passive immunity factors are divided into two groups:

Acquired, or artificial, immunity manifests itself in the process of ontogenesis, is not fixed in the offspring and acts during one, or less often, several growing seasons. To form acquired immunity to an infectious disease, plants are treated with biological and chemical immunizers. In biological immunization, treatment is carried out with weakened cultures of pathogens (vaccination) or their metabolites. For example, tomato plants infected with a weakly pathogenic strain of TMV are not subsequently affected by more aggressive strains of this virus.

Chemical immunization, as one of the methods of disease prevention, is based on the use of substances called resistance inducers, or immunomodulators.

They are able to activate defensive reactions. Some systemic drugs, phenol derivatives, chitosams, etc. have this effect. Registered immunomodulators also include drugs Narcissus, Immunocytophyte, etc.

The term “immunity” (means “freedom” from something) – complete immunity of the body to an infectious disease.

Currently, the concept of plant immunity is formulated as the immunity it exhibits to diseases in the event of direct contact of them (plants) with pathogens capable of causing a given disease when the conditions necessary for infection exist.

Along with complete immunity (immunity), very similar concepts are also distinguished - resistance or resistance and endurance or tolerance.

Those plants (species, varieties) that are affected by the disease, but to a very weak extent, are considered resistant (resistant).

Endurance (tolerance) they call the ability of diseased plants not to reduce their productivity (the quantity and quality of the harvest or to reduce it so slightly that it is practically not felt)

Susceptibility ( susceptibility) – the inability of plants to resist infection and spread of the pathogen in its tissues, i.e. ability to become infected upon contact with sufficient quantity infectious onset under appropriate external conditions.

Plants have all of the listed types of immunity.

Immunity (immunity) of plants to diseases can be congenital and be passed on by inheritance. This type of immunity is called natural immunity.

Innate immunity can be active or passive.

Along with natural immunity, plants may be characterized by acquired (artificial) immunity - the ability of plants not to be affected by one or another pathogen, acquired by the plant during the process of ontogenesis.

Acquired immunity can be infectious if it occurs in a plant as a result of recovery from a disease.

Non-infectious acquired immunity can be created using special techniques under the influence of treating plants or seeds with immunizing agents. This type of immunity has great importance in the practice of agricultural protection plants from diseases.

Increasing plant resistance to diseases using artificial methods is called immunization , which can be chemical and biological.

Chemical immunization is to use various chemical substances, capable of increasing plant resistance to disease. Fertilizers, microelements, and antimetabolites are used as chemical immunizers. Acquired non-infectious immunity can be created through the use of fertilizers. Thus, increasing the dose of potassium fertilizers increases the shelf life of root crops during storage.

Biological immunization consists of using other living organisms or their metabolic products (antibiotics, weakened or killed cultures of phytopathogenic organisms, etc.) as immunizers.

Plant resistance can be achieved by treating them with vaccines - weakened cultures of pathogens or extracts from them.

Lecture 5

Developmental biology of insects

Peculiarities external structure insects

2. Development of insects. Postembryonic development:

a) larval phase;

b) pupal phase;

B) the phase of an adult insect.

Development cycles of insects.

1. Features of the external structure (morphology) of insects.

Entomology is the science of insects (“entomon” - insect, “logos” - study, science).

The body of insects, like all arthropods, is covered on the outside with a dense cuticle. Forming a kind of shell, the cuticle is the exoskeleton of the insect and serves as good protection for it from adverse influences. external environment. The internal skeleton of the insect is poorly developed, in the form of outgrowths of the external skeleton. The dense chitinous cover is slightly permeable and protects the body of insects from loss of water and, consequently, from drying out. Exoskeleton Insects also have a support-mechanical role. In addition, internal organs are attached to it.

The body of an adult insect is divided into a head, thorax and abdomen and has three pairs of jointed legs.

The head consists of approximately five to six segments fused together; chest - out of three; the abdomen can have up to 12 segments. The size ratio between the head, chest and abdomen may vary.

Head and its appendages

The head bears a pair of compound eyes, often one to three simple eyes, or ocelli; movable appendages - antennae and mouthparts.

The shape of the head of insects is varied: round (flies), laterally compressed (locusts, grasshoppers), elongated in the form of a ready-made tube (weevils).

Eyes. The organs of vision are represented by complex and simple eyes. Complex, or faceted, the eyes, one pair of eyes, are located on the sides of the head and consist of many (up to several hundreds and thousands) visual units, or facets. In this regard, some insects (dragonflies, male flies and bees) have eyes so large that they occupy most of the head. Compound eyes are present in most adult insects and in larvae with incomplete metamorphosis.

Simple dorsal eyes, or ocelli, in a typical case, in number three are located in the form of a triangle on the forehead and crown between the compound eyes. As a rule, ocelli are found in adult, well-flying insects.

Simple lateral eyes, or stemmas, form two pairs of groups located on the sides of the head. The number of ocelli varies from 6 to 30. They are characteristic mainly of insect larvae with complete metamorphosis; they are less common in adult insects lacking compound eyes (fleas, etc.).

Antennae or antennae are represented by one pair of jointed formations located on the sides of the forehead between or in front of the eyes in the antennal fossae. They serve as organs of touch and smell.

Mouthparts have undergone significant changes from the gnawing type when feeding on solid food to various modifications of the sucking type when taking liquid food (nectar, plant juice, blood, etc.). There are: a) gnawing-licking; b) piercing-sucking; c) sucking and d) licking types of mouth organs.

The type of plant damage depends on the feeding method and the structure of the mouth organs, by which pests can be diagnosed and a group of insecticides can be selected to combat them.

Breasts and appendages

Breast structure. The thoracic region of the insect consists of three segments: 1) prothorax, 2) mesothorax, and 3) metathorax. Each segment, in turn, is divided into an upper half-ring—the back, a lower half-ring—the chest, and side walls—the barrels. The semirings are called: pronotum, prothorax, etc.

Each chest segment carries a pair of legs, and winged insects meso- and metathorax - a pair of wings each.

Structure and types of legs. The leg of an insect consists of: coxa, trochanter, femur, tibia and tarsus.

According to the lifestyle and level of specialization of individual groups of insects, they have Various types legs Thus, running legs, with elongated thin segments, are characteristic of cockroaches, bedbugs, ground beetles and other fast running insects; walking legs with shorter segments and widened tarsi are most typical of leaf beetles, longhorned beetles, and weevils.

Adaptation to living conditions or methods of movement contributed to the specialization of the front or hind legs. This is the case with mole crickets, which most of the time life cycle carried out in the soil, digging forelegs with a shortened and widened femur and tibia, and an underdeveloped tarsus appeared.

The hind legs of locusts, grasshoppers, and crickets have transformed into jumping legs, characterized by strong thickened femurs and the absence of a trochanter.

Plant immunity- this is their immunity to pathogens or inability to be damaged by pests.

It can be expressed in plants in different ways - from a weak degree of resistance to its extremely high severity.

Immunity- the result of the evolution of established interactions between plants and their consumers (consumers). It represents a system of barriers that limits the colonization of plants by consumers, which negatively affects the life processes of pests, as well as a system of plant properties that ensures their tolerance to violations of the integrity of the body and manifests itself at different levels of plant organization.

Barrier functions that ensure the resistance of both vegetative and reproductive organs of plants to the effects of pests, can perform growth and organ-forming, anatomical-morphological, physiological-biochemical and other characteristics of plants.

Plant immunity to pests manifests itself at various taxonomic levels of plants (families, orders, tribes, genera and species). For relatively large taxonomic groupings of plants (families and higher), absolute immunity (complete innocence of plants by this type of pest) is most characteristic. At the level of genus, species and variety, the relative importance of immunity is manifested predominantly. However, even the relative resistance of plants to pests, especially manifested in varieties and hybrids of agricultural crops, has important to suppress the number and reduce the harmfulness of phytophages.

The main distinguishing feature of plant immunity to pests (insects, mites, nematodes) is the high degree of expression of barriers that limit the choice of plants for feeding and oviposition. This is due to the fact that most insects and other phytophages lead a free (autonomous) lifestyle and come into contact with the plant only at certain stages of their ontogenesis.

It is known that insects have no equal in the diversity of species and life forms represented in this class. They have reached the highest level of development among invertebrate animals, primarily due to the perfection of their senses and movement. This provided insects with prosperity based on the wide possibilities of using high levels of activity and reactivity while conquering one of the leading places in the cycle of substances in the biosphere and in ecological food chains.

Well-developed legs and wings, combined with a highly sensitive sensory system, allow phytophagous insects to actively select and colonize food plants of interest to them for feeding and laying eggs.

The relatively small size of insects, their high reactivity to environmental conditions and the associated intense work of their physiological and, in particular, locomotor and sensory systems, high fertility and well-expressed instincts of “caring for offspring” require this group of phytophages, as well as other arthropods, extremely high energy costs. Therefore, we classify insects in general, including phytophages, as organisms with a high level of energy expenditure, and therefore also very demanding in terms of energy intake. energy resources with food, and the high fertility of insects determines their high needs for plastic substances.

One of the proofs of the increased demands of insects to provide energy substances can be the results of comparative studies of the activity of the main groups of hydrolytic enzymes in the digestive tracts of phytophagous insects. These studies, carried out on many species of insects, indicate that in all species examined, carbohydrases, enzymes that hydrolyze carbohydrates, were sharply distinguished in their comparative activity. The established relationships between the activities of the main groups of insect digestive enzymes reflect well appropriate level the needs of insects for basic metabolic substances - carbohydrates, fats and proteins. A high level of autonomy of the lifestyle of phytophagous insects from their food plants, combined with good developed abilities directional movement in space and time and a high level of general organization of phytophages were manifested in the specific features of the biological system of phytophage - food plant, which significantly distinguish it from the system of pathogen - food plant. These distinctive features indicate the greater complexity of its functioning, and hence the emergence of more complex problems when studying and analyzing it. In general, the problems of immunity are largely ecological and biocenotic in nature; they are based on trophic connections.

Coupled evolution of phytophages with forage plants led to the restructuring of many systems: sensory organs, organs associated with food intake, limbs, wings, body shape and color, digestive system, excretion, accumulation of reserves, etc. Food specialization gave an appropriate direction to metabolism different types phytophages and thus played a decisive role in the morphogenesis of many other organs and their systems, including those not directly related to the search, intake and processing of food by insects.

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BASICS OF PLANT IMMUNITY TO DISEASE

In the most severe epiphytotics, plants are affected by the disease unequally, which is associated with the resistance and immunity of the plants. Immunity is understood as absolute innocence in the presence of infection under conditions favorable for infection of plants and the development of diseases. Resilience is the ability of the body to withstand severe disease damage. These two properties are often identified, meaning that plants are weakly affected by diseases.

Resistance and immunity are complex dynamic states that depend on the characteristics of the plant, the pathogen and environmental conditions. The study of the causes and patterns of stability is very important, since only in this case is it possible successful work on breeding resistant varieties.

Immunity can be congenital (hereditary) or acquired. Innate immunity is passed on from parents to offspring. It changes only with changes in the genotype of the plant.

Acquired immunity is formed during the process of ontogenesis, which is quite common in medical practice. Plants do not have such a clearly defined acquired property, but there are techniques that can increase plant resistance to disease. They are being actively studied.

Passive resistance is determined by the constitutional characteristics of the plant, regardless of the action of the pathogen. For example, the thickness of the cuticle of some plant organs is a factor of passive immunity. Active immunity factors act only upon contact between the plant and the pathogen, i.e. arise (induced) during the pathological process.

The concept of specific and nonspecific immunity is distinguished. Nonspecific is the inability of some pathogens to cause infection of a certain plant species. For example, beets are not affected by pathogens of smut diseases of grain crops, potato late blight, potatoes are not affected by beet cercospora blight, grains are not affected by potato macrosporiosis, etc. Immunity that manifests itself at the variety level in relation to specialized pathogens is called specific.

Factors of plant resistance to disease

It has been established that resistance is determined by the total effect of protective factors at all stages of the pathological process. The whole variety of protective factors is divided into 2 groups: preventing the penetration of the pathogen into the plant (axenia); preventing the spread of the pathogen in plant tissues (true resistance).

The first group includes factors or mechanisms of a morphological, anatomical and physiological nature.

Anatomical and morphological factors. Barriers to the introduction of pathogens can be the thickness of the integumentary tissue, the structure of the stomata, the pubescence of the leaves, waxy coating, and structural features of plant organs. The thickness of the integumentary tissues is a protective factor against those pathogens that penetrate plants directly through these tissues. These are primarily powdery mildew mushrooms and some representatives of the Oomycetes class. The structure of stomata is important for the introduction into tissue of bacteria, pathogens of false powdery mildew, rust, etc. Usually, it is more difficult for the pathogen to penetrate through tightly covered stomata. The pubescence of leaves protects plants from viral diseases and insects that transmit viral infection. Thanks to the waxy coating on leaves, fruits and stems, drops do not linger on them, which prevents the germination of fungal pathogens.

Plant habit and leaf shape are also factors that inhibit the initial stages of infection. Thus, potato varieties with a loose bush structure are less affected by late blight, since they are better ventilated and infectious droplets on the leaves dry out faster. Fewer spores settle on narrow leaf blades.

The role of the structure of plant organs can be illustrated by the example of rye and wheat flowers. Rye is very strongly affected by ergot, while wheat is very rarely affected. This is explained by the fact that the scales of wheat flowers do not open and the spores of the pathogen practically do not penetrate into them. Open type flowering in rye does not prevent spores from entering.

Physiological factors. The rapid introduction of pathogens can be hampered by high osmotic pressure in plant cells, the speed physiological processes, leading to healing of wounds (formation of wound periderm), through which many pathogens penetrate. The speed of passage of individual phases of ontogenesis is also important. Thus, the causative agent of durum smut of wheat penetrates only into young seedlings, therefore varieties that germinate amicably and quickly are less affected.

Inhibitors. These are compounds found in plant tissue or synthesized in response to infection that inhibit the development of pathogens. These include phytoncides - substances of various chemical nature, which are factors of innate passive immunity. IN large quantities phytoncides are produced by the tissues of onions, garlic, bird cherry, eucalyptus, lemon, etc.

Alkaloids are nitrogen-containing organic bases formed in plants. Plants of the legume, poppy, nightshade, asteraceae, etc. families are especially rich in them. For example, solanine in potatoes and tomatine in tomatoes are toxic to many pathogens. Thus, the development of fungi of the genus Fusarium is inhibited by solanine at a dilution of 1:105. Phenols can suppress the development of pathogens, essential oils and a number of other compounds. All of the listed groups of inhibitors are always present in intact (undamaged tissues).

Induced substances that are synthesized by the plant during the development of the pathogen are called phytoalexins. By chemical composition all of them are low molecular weight substances, many of them

are phenolic in nature. It has been established that the plant’s hypersensitive response to infection depends on the rate of induction of phytoalexins. Many phytoalexins are known and identified. Thus, rishitin, lyubin, and fituberin were isolated from potato plants infected with the causative agent of late blight, pisatin from peas, and isocoumarin from carrots. The formation of phytoalexins represents a typical example of active immunity.

Active immunity also includes activation of plant enzyme systems, in particular oxidative ones (peroxidase, polyphenoloxidase). This property allows you to inactivate the hydrolytic enzymes of the pathogen and neutralize toxins.

Acquired, or induced, immunity. To increase plant resistance to infectious diseases, biological and chemical immunization of plants is used.

Biological immunization is achieved by treating plants with weakened cultures of pathogens or their metabolic products (vaccination). It is used to protect plants from certain viral diseases, as well as bacterial and fungal pathogens.

Chemical immunization is based on the action of certain chemicals, including pesticides. Assimilating in plants, they change metabolism in a direction unfavorable for pathogens. An example of such chemical immunizers are phenolic compounds: hydroquinone, pyrogallol, orthonitrophenol, paranitrophenol, which are used to treat seeds or young plants. A number of systemic fungicides have immunizing properties. Thus, dichlorocyclopropane protects rice from blast disease by enhancing the synthesis of phenols and the formation of lignin.

The immunizing role of some microelements that are part of plant enzymes is also known. In addition, microelements improve the supply of essential nutrients, which has a beneficial effect on plant resistance to disease.

Genetics of resistance and pathogenicity. Types of Resilience

The resistance of plants and the pathogenicity of microorganisms, like all other properties of living organisms, are controlled by genes, one or more, qualitatively different from each other. The presence of such genes determines absolute immunity to certain races of the pathogen. The causative agents of the disease, in turn, have a virulence gene (or genes) that allows it to overcome protective effect resistance genes. According to X. Flor's theory, for each plant resistance gene a corresponding virulence gene can be developed. This phenomenon is called complementarity. When exposed to a pathogen that has a complementary virulence gene, the plant becomes susceptible. If the resistance and virulence genes are not complementary, plant cells localize the pathogen as a result of a hypersensitive reaction to it.

For example (Table 4), according to this theory, potato varieties that have the R resistance gene are affected only by race 1 of the pathogen P. infestans or a more complex, but necessarily possessing virulence gene 1 (1.2; 1.3; 1.4; 1,2,3), etc. Varieties that do not have resistance genes (d) are affected by all races without exception, including the race without virulence genes (0).
Resistance genes are most often dominant, so they are relatively easy to pass on to offspring during selection. Hypersensitivity genes, or R-genes, determine the hypersensitive type of resistance, which is also called oligogenic, monogenic, true, vertical. It provides the plant with absolute invincibility when exposed to races without complementary virulence genes. However, with the appearance of more virulent races of the pathogen in the population, resistance is lost.

Another type of resistance is polygenic, field, relative, horizontal, which depends on the combined action of many genes. Polygenic resistance is inherent to varying degrees in each plant. At a high level pathological process slows down, which allows the plant to grow and develop, despite being affected by the disease. Like any polygenic trait, such resistance can fluctuate under the influence of growing conditions (level and quality of mineral nutrition, moisture supply, day length and a number of other factors).

The polygenic type of resistance is inherited transgressively, so it is problematic to fix it by breeding varieties.

A common combination of hypersensitive and polygenic resistance in one variety is common. In this case, the variety will be immune until the appearance of races capable of overcoming monogenic resistance, after which protective functions determines polygenic resistance.

Methods for creating resistant varieties

In practice, directed hybridization and selection are most widely used.

Hybridization. The transfer of resistance genes from parent plants to offspring occurs during intervarietal, interspecific and intergeneric hybridization. To do this, plants with the desired economic and biological characteristics and plants with resistance are selected as parent forms. Donors of sustainability are more often wild species, therefore, undesirable properties may appear in the offspring, which are eliminated by return crossings, or backcrosses. Beyer wasps repeat until all signs<<дикаря», кроме устойчивости, не поглотятся сортом.

With the help of intervarietal and interspecific hybridization, many varieties of grains, leguminous crops, potatoes, sunflowers, flax and other crops that are resistant to the most harmful and dangerous diseases have been created.

When some species do not cross with each other, they resort to the “intermediary” method, in which each type of parental form or one of them is first crossed with a third species, and then the resulting hybrids are crossed with each other or with one of the originally planned species.

In any case, the stability of hybrids is tested against a strict infectious background (natural or artificial), i.e., with a large number of pathogen infections, under conditions favorable for the development of the disease. For further propagation, plants that combine high resistance and economically valuable traits are selected.

Selection. This technique is a mandatory step in any hybridization, but it can also be an independent method for obtaining resistant varieties. By the method of gradual selection in each generation of plants with the desired characteristics (including resistance), many varieties of agricultural plants have been obtained. It is especially effective for cross-pollinating plants, since their offspring are represented by a heterozygous population.

In order to create disease-resistant varieties, artificial mutagenesis, genetic engineering, etc. are increasingly being used.

Causes of loss of stability

Over time, varieties, as a rule, lose resistance either as a result of changes in the pathogenic properties of pathogens of infectious diseases, or a violation of the immunological properties of plants during their reproduction. In varieties with a hypersensitive type of resistance, it is lost with the appearance of more virulent races or complementary genes. Varieties with monogenic resistance are affected due to the gradual accumulation of new races of the pathogen. That is why breeding varieties only with a hypersensitive type of resistance is futile.

There are several reasons contributing to the formation of new races. The first and most common are mutations. They usually pass spontaneously under the influence of various mutagenic factors and are inherent in phytopathogenic fungi, bacteria and viruses, and for the latter, mutations are the only way of variability. The second reason is the hybridization of genetically different individuals of microorganisms during the sexual process. This path is characteristic mainly of fungi. The third way is heterokaryosis, or heteronuclearity, of haploid cells. In fungi, heteronucleation can occur due to mutations of individual nuclei, the transition of nuclei from hyphae of different quality through anastomoses (fused sections of hyphae) and recombination of genes during the fusion of nuclei and their subsequent division (parasexual process). Heteronuclearity and the asexual process are of particular importance for representatives of the class of imperfect fungi, which lack the sexual process.

In bacteria, in addition to mutations, there is a transformation in which DNA isolated by one strain of bacteria is absorbed by the cells of another strain and is included in their genome. During transduction, individual chromosome segments from one bacterium are transferred to another using a bacteriophage (bacterial virus).

In microorganisms, the formation of races occurs constantly. Many of them die immediately, being uncompetitive due to a lower level of aggressiveness or lack of other important traits. As a rule, more virulent races become established in the population in the presence of plant varieties and species with genes for resistance to existing races. In such cases, a new race, even with weak aggressiveness, without encountering competition, gradually accumulates and spreads.

For example, when cultivating potatoes with resistance genotypes R, R4 and R1R4, races 1 will predominate in the population of the late blight pathogen; 4 and 1.4. When varieties with genotype R2 are introduced into production instead of R4, race 4 will gradually disappear from the pathogen population, and race 2 will spread; 1.2; 1,2,4.

Immunological changes in varieties can also occur due to changes in their growing conditions. Therefore, before zoning varieties with polygenic resistance in other ecological-geographical zones, they must be immunologically tested in the zone of future zoning.

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